The basis of this grant is our discovery of a novel tumor antigen (p40) that has several features, which make it an attractive candidate as a target for antibody-based immunotherapy of certain cancers. These features include: (1) Tumor specific expression; (2) Broad expression on many different tumors; (3) Antibody binding inhibits tumor proliferation and induces apoptosis. The objective of this grant is to develop and evaluate monoclonal antibodies against this tumor antigen for immunotherapy. Our underlying hypothesis is that tumor specific monoclonal antibodies which block proliferation and cause tumor cells to die have the potential to treat cancers. An important feature of our anti-tumor monoclonal antibody selected for these studies is that it reacts with (and is anti-proliferative and pro-apoptotic for) both murine and human tumors. Therefore, we can evaluate its ability to treat both murine and human tumors. The goal of the first Aim is to clone and characterize the p40 gene. The rationale for this objective is that it will allow us to define the molecular structure of this antigen. Moreover, it will provide an important tool to explore the function of this antigen. Our experimental approach will be to probe cDNA expression libraries with anti-ligand reagents or to probe libraries with oligonucleotides based on the amino acid sequence of p40. The goal of the second aim is to define which human tumors express the p40 antigen and to assess how these tumors are affected by the anti-p40 mAb. The obvious importance of this objective is that this data will determine the kinds of tumors that are candidates for immunotherapy with the anti-p40 mAb. Our experimental approach is to analyze expression of the p40 antigen in a variety of biopsies and surgically-resected tumors by immunohistochemistry. We will also examine whether p40 is expressed in any normal tissues. The effects of the mAb on cell proliferation and apoptosis of p40 positive cells will be examined in vitro. Finally, we will determine whether tumors can extinguish the expression the p40 antigen, and if so, how this loss of expression affects the malignant phenotype of the tumor. The goal of the third aim is to test whether the anti-p40 antibody can cause regression of or cure established cancers in an animal model. Our experimental approach will be to inject the anti-p40 mAb into mice bearing transplanted tumors. In one set of experiments we will test the efficacy of immunotherapy on mice transplanted with syngeneic tumors. In another set of experiments, we will test the effect of p40 on human tumors transplanted into immunodeficient mice.